Sound reproducing system



C. TAPPAN July 27, 1937.

Filed Dec. 16, 1932 SOUND REPRODUCING SYSTEM INVENTOR J ATTORNEY Patented July 27, 1937 UNITED STATES PATENT OFFICE SOUND REPRODUCING SYSTEM Chester Tappan, New York, N. Y., assignor to General Talking Pictures Corporation, New York, N. Y., a corporation of Delaware Application December 16, 1932, Serial No. 647,690 3 Claims. (01. 179-4003) The present invention relates to improvements act as a conventional type of filter or smoothing in sound reproducing systems, one object of the circuit. invention being the provision of a system oper- Referring now to leads I and 2' following ated from an alternating current source so as through rectifiers I2 and I3 to leads I9 and 20' to displace or replace storage batteries with a which in turn are connected to ground and to 5 source, a supply derived from commercial alterlead 2I respectively, we have a duplicate circuit nating current circuits, and so arrange the comthroughout, the output of which is, as mentioned, ponent parts as to produce the necessary and parallel to the output of the first supply system. desired results, that is, to produce a supply of Lead 2I is connected to: the common point of rectifier current in the system which is practiswitch 22 which transfers from contact 23 to 10 cally as constant as the supply from the storage 23' or vice versa and hence through lead 25 or batteries. 26 to exciting light 2! or 21, the other side Another object of this invention is the proof which is connected through switch 25 or 25' vision of a system of this character in which the to ground, thereby completing the circuit. I installation is exceedingly simple so as to pro- Coming back to leads 3I and 32 connecting l5 duce a commercially successful system. the alternating current source of supply to the With the foregoing and other objects in View, primary of power transformer 33, the secondary which will appear as the description proceeds, of which is connected through leads 34 and 35 the invention resides in the combination and and through leads 36 and 31 to rectifier elements in arrangement of parts and in the details of con- 42 and 43 respectively. The output of these struction hereinafter described and claimed, it rectifiers is connected in parallel through leads being understood that changes in the precise em- 39 and 40 and 38 and M through choke coil 44 bodiment of the invention herein disclosed can and lead 49, through choke coil 44 and choke be made within the scope of what is claimed coil 45-to lead 50. Condensers 46, 4'! and 48 17, without departing from the spirit of the invenare so inter-connected in conjunction with choke tion. I coils 44 and 45 so as to act as a conventional In the accompanying drawing is illustrated filter or smoothing circuit. Lead 49 connects to and shown a diagrammatic view of a complete the terminal 52 and lead 50 connects to the sound reproducing system made according to and terminal 5|. Lead 54 connects terminal 52 to :lo embodying the present invention. one side of, the filaments of the vacuum tubes Referring to drawing: II, "l2, l3 and I4. It also connects through lead The leads I8I and I82 constitute the alternat- 68 ,to ground. Terminal 5I is connected through ing current mains. I rom here this current is leads 53 and 57 to the other side of filament tubes passed through main switch I80 which turns all II, I2, I3 and 14, thereby completing the filament 3-,; the power on or off, through fuses I18 and I19, circuit for the tubes just mentioned. It is also through leads I76 and Ill to leads I15 and. I14 connected through lead 59 to condenser 70 the which are common, to the primaries of all power other side of Which is connected to ground. This transformers. These leads in turn connect minus-A circuit is also connected through lead through leads I and 2 to the primary of power 55 to choke coil 56, from choke coil 56 to ter- 10 transformer 3, from the secondary of this transminal 51 hence through lead 58 to terminal 59' former throughleads 4 and 5 to rectifier unit I2, and through lead BI to terminal 59, from terand through leads 5 and 'I to rectifier unit I3. minal 59 through lead 50 to resistance 62, hence I You will note that these rectifiers are arranged through resistor 63, through resistor 64 to filain the conventional manner so that the alternatment of tube 65; from the other side of the filaing current will only flow through the correct ment of this tube through lead 2I5 to the fila- 45 path, and the output on these rectifiers is pulsatment of tube 66, the other side of which is coning direct current. The outputof rectifier I3 nected through lead 2I6to terminal 2I'I then is connected 'to the output of rectifier I 2 through through lead 2I8 to terminal 211', through lead leads I0 and II. The output of rectifier I2 in 2I8' to ground, completing the circuit. The turn is connected through lead 9 to choke I4, above circuit is duplicatedfrom terminal 50 and through leads 8 and I9 to ground. The through lead 60, resistors 62', 63', 64' to tubes current then passes through choke coils I4 and 65 and 68 hence back to 2H and through 2I8 I 5, through lead'ZII to lead 2|. The condensers to ground. This gives us our low voltage fila- I 6 ,"I7and I8 are connected in such a manner ment supply for the tubes of the photocell am- 55 and in conjunction with choke coils I4 and I5 plifiers. It will be further noted that this cir- 5 2 cuit is by-passed to ground through condensers 2I9 and 2I9 to ground Leads IBI and I62 connect to the primary of transformer I63, the secondary of which is connected to leads I64 and 55, to rectifier IBI the output of which is connected to leads I68 and I66 to condenser I59, which acts as a filter or smoothing condenser hence through leads I10 and I'll to the field I12 of the dynamic speaker I13. You will further note that this circuit is duplicated for dynamic speaker H3.

The high voltage or B supply for the photo cells, photo cell amplifiers and intermediate amplifiers will now be described. Leads I5 and I6 are connected to primary of transformer II. The high voltage winding is connected as shown to plates of tube I8, filament of which is connected to the low voltage winding on the secondary of transformer 5?. The mid-point of this low voltage winding is connected through lead is to choke coil 85. The mid-point of the high voltage winding is connected through lead 86, one side of condensers 3i, 3?. and 83, one side of voltage divider 84-, one side of condenser 8i, one side of condenser 88, hence through lead 9| to ground. Lead I9 as Well as connecting to choke also connects to the other side of condenser 8i. Choke coil 85 is then connected to choke coil 8% and the other side of condenser 82. The other side of choke coil 36 is connected to the other side of condenser 83 and to the other side of voltage divider 8 3, to the other side of condenser 8? and through the lead 89 to the plus P. E. C. terminal 92. A tap on voltage divider 84 is led to the other side of condenser 8%, hence through lead 9th to plus B terminal 93 on the intermediate amplifier. You will please note that the combination as shown, of choke coils B5 and 86, condensers 3!, S2, S3, 8? and 88 and voltage 2 divider 8 3, is the conventional type of filtering or smoothing system and distribution system. From terminal Q2 on the intermediate amplifier the current is then led to terminal ill, from here through lead $34, to terminal 39, through lead EEH to terminal 99 through lead IE2 to one side of potentiometer I03, the other side of which is connected through resistor N34 to ground. The adjustable point on potentiometer W3 is led through lead 101 to condenser I65, the other side i of which is grounded. This variable point is also led through lead MB to photo cell 3i the other side of which is connected through lead 2H] to one side of resistor I84 through leads me and 22 I, through resistors 53 and 64 to filament of tube 65 a and through lead "M5, through filament of tube of transformer H53 goes to 65 through leads 2H5 and 222 to ground. From terminal 99' we duplicate the circuit through lead It?! to potentiometer I63 etc. This is for the second photo cell. From terminal 93 connected through to terminal 96 through lead 95 to terminal 98 through lead 580 to terminal 98, through lead Its to the primary winding of trans former lid and through lead II2 to the primary of transformer I I I. The othersideof thiswinding the plate of tube 65 hence to filament of tube 65 through lead 2 E 5 and through filament of tube 56 through lead 256 and lead 222 to ground. From the other side of the primary winding on transformer II I current passes to the plate of tube 66 hence to the filament of tube 66 to leads 2I6 and 222 to ground. From terminal 98 through lead I519 etc. This circuit is duplicated for the plate supply of the other photo cell amplifier.

Leads 85 and I6 are connected to the primary of transformer 11'. The high voltage winding of this transformer is connected to the plates of tube I8 as shown. The low voltage winding is connected to the filament of this tube The midpoint of this low winding is connected by lead I9, to choke coil 85. The mid-point of the high voltage winding is connected through lead to one side of condensers BI, 82 and 83, and one side of voltage divider 84 and one side of condenser H5. Lead '13 also connects to the other side of condenser ill. The other side of choke coil 85 is connected to choke coil 86 and to the other side of condenser 82'. The other side of the choke coil 86 is connected to the other side of condenser 82a and to the other side of the voltage divider 84, also to one side of condenser II4. This constitutes the usual rectifier and filter combination or smoothing circuit and voltage distributor. At a point part way up the voltage divider 84 is connected to the other side of condenser H4 and the other side of condenser H5, and to one side of condensers I I6 and I I1, through lead IIB to ground. Lead Bil as previously pointed out connects to one side of voltage divider 84' and from here through lead Hi) to terminal H23 on the intermediate amplifier. A point on the voltage divider 223 is connected through lead I26 to the other side of condenser Ill and hence to terminal 921. Point 224 on the voltage divider is connected through lead condenser H6 and to terminal I22 of the intermediate amplifier. Point 228isconnected through lead 2I to terminal I29 of the intermediate amplifier. Terminal I23 of the intermediate amplifier is connected through lead suppressor resistor I32 to the secondary of transformer I91 and to one side of resistor I98, the other side of which is connected to grid of tube I3 and through lead 225 and through resistor 203 to the grid of tube I4. Terminal I21 of the intermediate amplifier is connected through lead I28, through resistor IBI, through lead 226, through resistor I93, and through the secondary of transformer I92 to the grid of tube II, through lead 22! and through resistor I95 to the grid of the tube I2. These two circuits complete the C bias arrangement for the tubes of the intermediate amplifier. Terminal I22 is connected through lead I24, through choke coil I38 to plate tube I2 and through choke coil IN to plate of tube II, hence to filaments of tubes I2 and II respectively, hence back to ground through lead 68. Terminal I29 is connected through lead I30 and through choke coils I39 and I40 to plates of tubes I3 and I4 respectively, hence through the filaments of these tubes back to ground through lead 68. This completes the B circuits for the intermediate amplifier.

Leads MI and I42 are connected to the primary of transformer I43 the secondary of which has three windings. One low voltage winding is connected through leads I55 and I56 to the filaments of tubes. I59 and I653. The mid-point of this winding is connected through resistor I5I to ground I52. The mid-point is also connected to one side of condenser I50 the other side of which is connected to ground. This is the grid biasing resistor. The other low voltage winding is connected to the filaments of the rectifier tubes I44 the mid-point of which is connected through lead I45 to choke coil I41. The high voltage winding on the secondary transformer I43 is connected to the plates of the rectifier tubes I44. The mid-point of this high voltage winding is connected through leads I46 and I52 to ground. It is also connected I20 to the other side of 1'.

I 25, through to one side of condensers I48 and I49. The ground is then carried through lead I 53 to the mid-point of the secondary of transformer I51 and hence through this transformer to the grids of tubes I59 and IE0. At the same point on choke I41 where lead I45 connects with this choke coil it is also connected to the other side of condenser MB, and the other side of this choke coil I 41 is connected to the other side of condenser hi9, hence the B voltage is connected through lead I54 to the mid-point of the primary of transformer I58 hence to the plates of tubes I59 and I 60, from the plates to the filaments and from the filaments back to ground, thereby completing the circuit. This rectifier just described, plus the amplifier constitute a single unit; in other words, a complete power amplifier with its power pply.

Referring to leads I II and I42, transformer I43 etc., and including duplicate amplifier as shown directly above one previously described, constitutes the second complete power amplifier including its own power supply. You will further note that these constitute the usual power supply rectifier filtering and smoothing circuit and amplifying circuit.

The operation-The previously described method of lighting the exciting lamps 21 and 21 is used. You will note the film advancing mechanisms 225 and 29 and 28 and 29, also optical sys tems interposed for focusing the light on film 38. For a matter of convenience one machine only is described. The film 30 with the usual sound track is interposed between the exciting lamp 21, optical system, and, the photo cell 3i wherein the changes in the light intensity on photo cell 3| cause the fluctuation in the current passed by cell 3|, and from here out through lead 2! 9 to condenser I83 and hence to grid tube 65. The

other side of the photo cell is connected through leads Hi6 and I01 through condenser I05 and lead I68 to ground, this side of the circuit being carried through on ground throughout the entire circuit. Grid of tube 65 is thereby registering the difference in potentiality also across resistor I85. From tube 65 through transformer I I I] to grid of tube 66 through transformer III, through leads I 88 and I89, through attenuator I81, through leads I90 and IQI, through transfomer I92 to grid of tube 11, through condenser 94 to grid of tube 12, through condenser Ifit and through transformer I91 to grid of tube 13 and parallelled through lead 225 and resistor 2&3 and condenser 204 to grid of tube 14. The output of .tube 13 is connected through condenser I99 and potentiometer Zilll to transformer I51, the secondary of this transformer is connected to the grids of tubes I59 and Hill. The plates of these tubes are connected through transformer I58 and through leads 206 and 281 to magnetic speakers 205 and 205. These units are on horns 2% and 268. Duplicating the circuit from tube 14 connected through lead I40 to condenser 202 and to potentiometer 2M hence through transformer I51 to grids of tubes I59 and I 6t, from the plates of these tubes through transformer I58, and through leads 2H] and El I, to a step-down transformer 209, hence through leads 2I2 and 2I3 to the voice coils 2I4 and 2" of dynamic units I13 and I13.

From the foregoing description taken in connection with the drawing it is evident that there is here illustrated and described a system for reproducing sound from a photographic film as in theatrical and educational installations, that includes a source of illumination, the necessary photo electric cell, photographic sound record with its operating mechanism so that the film travels between the source and the cell, a source of alternating current and means for rectifying and filtering the same for said source of illumination, a filter being arranged to reduce the variations in the current supply of said source of illumination to such an extent that the effect of such variations is less than the effect of variations in the remainder of the system. Thus the alternating current from the usual lighting mains could be utilized in lieu of storage batteries for operating the complete sound reproducing system. The rectified current being used in this instance for the exciter lamp, the photoelectric cell for the necessary amplifiers and for the loud speakers, there being filters disposed throughout the system and operated from the source of alternating current to reduce the variations in said current. By this means a satisfactory reproduction of sound is produced without the usual noise due to alternating current or rather the irregularities therein, as would be the case if raw alternating current were used instead of a rectifier current as in the present instance.

What is claimed is:

1. In a sound reproducing system, the combination with an alternating current main and a plurality of rectifiers connected therewith, a

photographic sound record, means to progressively move said record, an exciter lamp and a photoelectric cell between which said record passes, a filter interposed between the exciter lamp and one of the rectifiers, a thermionic amplifier controlled from said photoelectric cell, and a filter interposed between another of said rectifiers and the photoelectric cell, and also connecting the filaments of the thermionic tubes of said amplifier to the same rectifier to which the photoelectric cell is connected.

2. A sound reproducing system as claimed in claim 1 wherein a thermionic power amplifier is connected to the output of the cell controlled thermionic amplifier, filters disposed between another of said rectifiers and connecting the filaments of the thermionic tubes of the power amplifier and a filter interposed between a fourth rectifier and the transformers and grid and plate elements of the power amplifier.

3. A sound reproducing system as claimed in claim 1 wherein a power amplifier is connected to the output of the cell controlled thermionic amplifier, a filter connected to a third rectifier and to the transformers and plate elements of the power amplifier, a filter connected between a fourth rectifier and the filaments of the thermionic tubes of the power amplifier, a loud speaker connected to the output of the power amplifier and having its exciting coil connected through a fifth rectifier.

CHESTER TAPPAN. 

